Quantitative Analysis Of Runoff Variations As Affected By Climate Variability And Human Activity In The Xilin River Basin

Xilin River Basin is the most representative region in the plateau basin of inland river basin in China.With the increase of climate change and the intensity of human activities,there is a shortage of water resources in the continental grassland basin of the plateau,the ecological environment is deteriorating,and hydrology in many river basins is deteriorating.The process has undergone changes that cannot be ignored.The academia has attributed the changes in runoff in the basin to the combined effects of climate and human activities.Therefore,quantitative analysis of the effects of climate change and human activities on the runoff of continental rivers in the plateau and the evolution of simulated runoff have become hydrology and water scientists' focus in the 21 st century.This paper takes the semi-arid inland river basin of Inner Mongolia as a typical research object,based on hydrological,meteorological,and socioeconomic data,the evolution of runoff in the Xilin River Basin was calculated using the methods of cumulative anomaly,double-accumulation curve,improved MK trend test,cumulant slope change rate comparison,and wavelet transform.The analysis has quantitatively calculated the contribution of climate change and human activities to runoff changes,and tried to use BP neural network model and SWAT model to simulate the time series evolution of runoff.The purpose of this study is to explore the watershed hydrological effects in the socio-economic development of northern semi-arid regions represented by the Xilin River Basin.The main results are as follows:1.From the chronological scale,annual runoff in the Xilin River Basin was the largest in the 1990 s,and it was the lowest in the early 21 st century,especially in the early 21 st century relative to the 1990 s,which was 54.90%.On the annual time scale,the runoff in the catchment has been declining significantly over the years.The runoff reached the maximum value in 2012,there was no maximum runoff in the year with the largest precipitation,and the smallest runoff was in the year with the smallest precipitation.On the seasonal scale,the runoff in the wet season is significantly less than that in the dry season,but the precipitation in the wet season is much larger than that in the dry season.This may be due to the formation of spring snowfall in the basin's snowmelt and river network storage and thawing increased runoff in the basin.Overall,in the changing environment,regardless of the time scale,runoff showed a significant downward trend from 1963 to 2015 in the Xilin River Basin.2.The annual runoff of the Xilin River Basin under a changing environment shows a significant downward trend,while the overall change trend of precipitation is not obvious;the relationship between precipitation and runoff before 1998 is different from the relationship between precipitation and runoff after 1998,the intensification of human activities has changed the mechanism and laws of natural runoff since 1998;There are 6-year and 25-year cycles of annual runoff and dry season runoff,and there is no significant period of runoff in the analysis season,this shows that it follows a larger cycle of change.3.Human activities mainly affect the characteristics of runoff changes in semi-arid grasslands in different time scales(hydrological year or season).The annual runoff in the Xilin River Basin was positively correlated with the precipitation and relative humidity in the climate factors,and negatively correlated with evaporation and all human activities;There was a significant positive correlation between precipitation,precipitation days,maximum precipitation intensity,mean precipitation intensity,and relative humidity in the wet season and negative correlations with wind speed and temperature,and negative correlation with all factors of human activities.The dry season runoff was significantly positively correlated with the relative humidity in the climate indicator alone,negatively correlated with temperature,and negatively correlated with population,GDP,PIP,and SIP in human activities.4.The key factor causing the decrease of runoff in the Xilin River Basin is human activity.Its contribution to the reduction of runoff is 59.66%.Socioeconomic factors such as population increase,animal husbandry and industrial development all affect the runoff of the basin.The contribution of climate fluctuations to the reduction of runoff was 40.34%,which contributed relatively little to the reduction of runoff in the study river basin.5.Based on the model simulation input factors selected by statistical correlation test,the BP neural network model was used to simulate the non-linear function relationship between runoff and climate and human activity factors in the Xilin River Basin,and a good simulation effect was obtained,indicating that the neural network applicability of the model to the simulated evolution of the runoff in the basin is good,especially when the distributed hydrological simulation cannot be achieved,this method can be applied to the basin.6.Based on the hydrological and meteorological data of the Xilin River Basin,DEM data,soil and land use data,a SWAT model of the catchment was established to simulate the annual runoff in the Xilin River Basin.The results showed that: the evaluation index efficiency coefficient of runoff simulation results(Ens),correlation coefficient(R2)and relative error(Re)are between 0.64-0.67,0.61-0.64 and 14.8%-19.6% respectively.This result indicates that the measured runoff is in good agreement with the simulated runoff.